1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Related Art
Generally, a method for manufacturing a semiconductor element includes many processes such as a process to deposit a plurality of materials on a silicon wafer as a film to be processed and a process to form a desired pattern on the film to be processed. Hereinafter, the process to form a pattern on the film to be processed will be explained. First, a resist film is formed by coating the surface of the film to be processed with a photosensitive material which is generally called a resist. Next, a predetermined region of the resist film is exposed. Next, the exposed region or an unexposed region of the resist film is removed in a development process to form a resist pattern. Further, dry etching is performed on the film to be processed by using the resist pattern as an etching mask. In this way, the pattern is formed on the film to be processed.
In recent years, with the miniaturization of patterns, immersion lithography capable of achieving a high NA (numerical aperture) has been used. In the immersion lithography, immersion exposure is performed by providing an immersion liquid (for example, pure water) between an exposure lens and the surface of the resist film. Further, in the immersion lithography, the immersion exposure is performed on a predetermined region by scanning the surface of the resist film with the exposure lens and the immersion liquid, which is called scanning exposure. Since the resist film contacts with the immersion liquid, a resist film (topcoatless resist film) for the immersion lithography process is developed to perform the scan with the exposure lens and the immersion liquid at high speed.
After the immersion exposure is performed, the edge of the resist film (namely, a peripheral region of the resist film formed on the surface of the wafer) remains the unexposed region. When a positive type resist is used, there is a case where the unexposed region is not removed to be left in the development process. Accordingly, wafer edge exposure (WEE) and the immersion exposure are performed on the edge of the resist film in the above order before the edge of the resist film is removed in the development process (see JP-A 2006-235230 (Kokai), for example).
However, when the wafer edge exposure is performed before the immersion exposure as in the conventional way, there is a problem that the edge of the resist film has a different film quality from the other regions of the resist film during the immersion exposure.